#region 添加水印

        /// <summary>

        /// 添加文字水印

        /// </summary>

        /// <param name="image"></param>

        /// <param name="text"></param>

        /// <param name="fontSize">字体大小</param>

        /// <param name="rectX">水印开始X坐标（自动扣除文字宽度）</param>

        /// <param name="rectY">水印开始Y坐标（自动扣除文字高度</param>

        /// <param name="opacity">0-255 值越大透明度越低</param>

        /// <param name="externName">文件后缀名</param>

        /// <returns></returns>

        public static Image AddTextToImg(Image image, string text, float fontSize, float rectX, float rectY, int opacity, string externName)

        {

            Bitmap bitmap = new Bitmap(image, image.Width, image.Height);

            Graphics g = Graphics.FromImage(bitmap);          

            //下面定义一个矩形区域

            float rectWidth = text.Length * (fontSize + );

            float rectHeight = fontSize + ;

            //声明矩形域

            RectangleF textArea = new RectangleF(rectX - rectWidth, rectY - rectHeight, rectWidth, rectHeight);

            Font font = new Font("微软雅黑", fontSize, FontStyle.Bold); //定义字体

            Brush whiteBrush = new SolidBrush(Color.FromArgb(opacity, , , )); //画文字用

            g.DrawString(text, font, whiteBrush, textArea);

            MemoryStream ms = new MemoryStream();

            //保存图片

            switch (externName)

            {

                case ".jpg":

                    bitmap.Save(ms, ImageFormat.Jpeg);

                    break;

                case ".gif":

                    bitmap.Save(ms, ImageFormat.Gif);

                    break;

                case ".png":

                    bitmap.Save(ms, ImageFormat.Png);

                    break;

                default:

                    bitmap.Save(ms, ImageFormat.Jpeg);

                    break;

            }

            Image h_hovercImg = Image.FromStream(ms);

            g.Dispose();

            bitmap.Dispose();

            return h_hovercImg;

        }

        /// <summary>

        /// 添加图片水印

        /// </summary>

        /// <param name="image"></param>

        /// <param name="text"></param>

        /// <param name="rectX">水印开始X坐标（自动扣除图片宽度）</param>

        /// <param name="rectY">水印开始Y坐标（自动扣除图片高度</param>

        /// <param name="opacity">透明度 0-1</param>

        /// <param name="externName">文件后缀名</param>

        /// <returns></returns>

        public static Image AddImgToImg(Image image, Image watermark, float rectX, float rectY, float opacity, string externName)

        {

            Bitmap bitmap = new Bitmap(image, image.Width, image.Height);

            Graphics g = Graphics.FromImage(bitmap);

            //下面定义一个矩形区域

            float rectWidth = watermark.Width + ;

            float rectHeight = watermark.Height + ;

            //声明矩形域

            RectangleF textArea = new RectangleF(rectX - rectWidth, rectY - rectHeight, rectWidth, rectHeight);

            Bitmap w_bitmap = ChangeOpacity(watermark, opacity);

            g.DrawImage(w_bitmap, textArea);

            MemoryStream ms = new MemoryStream();

            //保存图片

            switch (externName)

            {

                case ".jpg":

                    bitmap.Save(ms, ImageFormat.Jpeg);

                    break;

                case ".gif":

                    bitmap.Save(ms, ImageFormat.Gif);

                    break;

                case ".png":

                    bitmap.Save(ms, ImageFormat.Png);

                    break;

                default:

                    bitmap.Save(ms, ImageFormat.Jpeg);

                    break;

            }

            Image h_hovercImg = Image.FromStream(ms);

            g.Dispose();

            bitmap.Dispose();

            return h_hovercImg;

        }

        /// <summary>

        /// 改变图片的透明度

        /// </summary>

        /// <param name="img">图片</param>

        /// <param name="opacityvalue">透明度</param>

        /// <returns></returns>

        public static Bitmap ChangeOpacity(Image img, float opacityvalue)

        {

            float[][] nArray ={ new float[] {, , , , },

                                new float[] {, , , , },

                                new float[] {, , , , },

                                new float[] {, , , opacityvalue, },

                                new float[] {, , , , }};

            ColorMatrix matrix = new ColorMatrix(nArray);

            ImageAttributes attributes = new ImageAttributes();

            attributes.SetColorMatrix(matrix, ColorMatrixFlag.Default, ColorAdjustType.Bitmap);

            Image srcImage = img;

            Bitmap resultImage = new Bitmap(srcImage.Width, srcImage.Height);

            Graphics g = Graphics.FromImage(resultImage);

            g.DrawImage(srcImage, new Rectangle(, , srcImage.Width, srcImage.Height), , , srcImage.Width, srcImage.Height, GraphicsUnit.Pixel, attributes);

            return resultImage;

        }

        #endregion

Image img = Image.FromStream(file.InputStream);

string externName = Path.GetExtension(file.FileName);

//添加文字水印

System.Drawing.Image t_img = Upload.AddTextToImg(img, "我是水印",14.0f, img.Width - , img.Height - , , externName);

//添加图片水印

Image watermark =

Image.FromFile(Server.MapPath("/content/images/common/logo_main.png"));//水印图片

System.Drawing.Image t2_img = Upload.AddImgToImg(img, watermark, img.Width - , img.Height - , 0.5f, externName);